The present invention relates to a noise reduction system in which the high and low frequency parts of the spectrum of a signal are emphasized respectively by series connected variable frequency type filters prior to transmission or recording and upon reception or reproduction the corresponding frequency parts of the emphasized signal are de-emphasized respectively by series connected variable frequency type filters.
In a prior art noise reduction system, the spectrum of a signal is divided into different frequency bands by filters at a transmitter or recorder and the frequency divided components are controlled by variable gain amplifiers respectively in response to their amplitudes and combined in an adder to generate an output signal which is negatively summed with the original signal so that the latter is compressed in amplitude. At a receiver or reproducing apparatus, the received signal is divided into frequency bands corresponding to the frequency bands of the transmitter and the frequency divided components are controlled by variable gain amplifiers respectively in response to their amplitudes and combined in an adder to generate an output so that the amplitude of the received signal is expanded to restore the original signal. This prior art system however is susceptible to drop-outs or relatively large level fluctuations and tends to degrade its frequency response characteristic if there is a discrepancy between the cut-off frequencies of the frequency dividing filters.